Electric slag refining plant

ABSTRACT

The plant comprises an ingot mold, a plurality of fusible electrodes and a plurality of electrical supply conductors connected to respective ones of said electrodes and incorporating each a contact ammeter having a contact, which is arranged to operate when the current in the associated conductor is below a predetermined minimum. Said contacts are connected in series. An electrode holder carries said fusible electrodes and is movable to feed said electrodes into said mold. Electrically operable feed drive means are connected in series with said contacts and arranged to move said electrode toward said mold when all said contacts are in an operating condition.

United States Patent [191 Fischer 1 ELECTRIC SLAG REFINING PLANT [75] inventor: Ernst Fischer, Vienna, Austria [73] Assignee: Gebr. Bohler & Co. AG, Vienna,

Kapfenberg, Austria [22] Filed: June 23, 1972 [21] Appl. No.: 265,638

[30] Foreign Application Priority Data Sept. 17, 1971 Germany P 21 46 551.0

[52] US. Cl. 13/9, 13/13 [5 1] Int. Cl. H05b 7/00, HOSb 3/60 [58] Field of Search 13/9 ES, 13, 12

[56] References Cited I UNITED STATES PATENTS 3,217,205 11/1965 Bennett 13/13 X 3,300,712

l/l967 Segsworth 13/12 X -[11] 3,743,749 [451 July 3,1973

3,431,344 3/1969 Borrebach 13/12 Primary ExaminerRoy N. Envall, Jr. Attorney-Arthur O. Klein [5 7] ABSTRACT The plant comprises an ingot mold, a plurality of fusible electrodes and a plurality of electrical supply conductors connected to respective ones of said electrodes and incorporating each a contact ammeter having a contact, which is arranged to operate when the current in the associated conductor is below a predetermined minimum. Said contacts are connected in series. An electrode holder carries said fusible electrodes and is movable to feed said electrodes into said mold. Electrically operable feed drive means are connected in series with said contacts and arranged to move said electrode toward said mold when all said contacts are in an operating condition.

11 Claims, 1 Drawing Figure ELECTRIC SLAG REFINING PLANT This invention relates to apparatus for controlling the feeding ofa plurality of fusible electrodes which are secured to the same holder and, if desired, the movement of a liftable ingot mold, in plants for the electric slag refining of metals, particularly steels.

For the electric slag refining of metals, plants are known in which a plurality of, e.g., three fusible electrodes are secured to the same holder. This involves the disadvantage that the fusible electrodes fuse down irregularly so that trouble arises in.the operation of the plant. It is an object of the invention to avoid the above-mentioned disadvantage and to provide apparatus for controlling the feeding of a plurality of fusible electrodes which are secured to the same holder and used in electric slag refining; this apparatus should ensure a substantially uniform fusing down of the electrodes. This is accomplished according to the invention in that a contact ammeter is provided in each of the electrical conductors connected to the fusible electrodes, and these ammeters have contacts which are connected in series and in response to a decrease in current to predetermined values, cause the means for feeding the electrode holder and, if desired, means for lifting the ingotmold to operate.

If these fusible electrodes differ in cross-section, it will be desirable if the contacts of the ammeters are set to be responsive to currents which are approximately proportional to the cross-sectional areas of the respective fusible electrodes.

Further details of the apparatus according to the invention will become apparent from the following description of an embodiment which is shown diagrammatically and by way of example on the accompanying drawing, which is an elevation showing a plant for the electric slag refining of steels.

Three fusible electrodes are insulated from each other and secured to the same holder 1 1. Each of these electrodes is connected to one of the phase conductors R, S, T of a three-phase a.c. system. Each of these conductors R, S, T incorporates a contact ammeter 71. The above-mentioned threephase a.c. system may be constituted, e.g., by the secondary windings of a threephase a.c. transformer. The fusible electrodes 10 consist of steel and are preferably cylindrical and are immersed in a slag layer 60, which is provided in an ingot mold 20, which is, e.g., cylindrical. The electrodes are fused down under the action of the heat generated by the electric currents flowing through the electrodes. The resulting molten steel 31 solidifies in the liquidcooled ingot mold 20 to form a solid ingot 30. The neutral conductor N of the three-phase a.c. system is connected to the bottom plate 40, which consists preferably of copper and supports the ingot 30. The electrode holder 11 and the ingot mold 20 are secured to respective lifting carriages 12 and 23 andtogether with the respective lifting carriages are vertically movable along a guide column 50 by means of respective rope drives. Each rope drive comprises an electric gearmotor 13 or 24, a rope drum 14 or 25, which is secured to the stub shaft of the gearmotor, and a wire rope 15 or 26, which is secured at one endto the associated lifting carriage 12 or 23 and at the other end to the respective rope drum 14 or 25. The two gearmotors 13 and 24 are provided with self-locking gears and mounted at the top end of the column 50.

An electric lead extends from the phase conductor R via the contacts 71' of the ammeters 71 to a point at which two leads 72 and are branched off. The ammeter contacts 71 are thus connected in series. Each of the leads 72 and 75 extends via the controlled contact 73" or 76" of a pulse-controlled relay 73 or 76 and the exciting winding 16 or 27' ofa three-phase a.c. contactor 16 or 27 to the neutral conductor M of the above-mentioned three-phase a.c. system. Each of the contactors 16 and 27 controls the supply of current to one of the gearmotors l3 and 24 and for this purpose the normally open contact 16" or 27 of the contactor 16 or 27 is incorporated in the supply leads R1, S1, T1 or R2, S2, T2 of a three-phase a.c. system. The exciting windings 73' and 76' of the pulse-controlled relays 73 and 76 are connected to a known pulse generator 78, which is mechanically or electronically adjustable and connected between the phase conductor R and the neutral conductor M. Whereas the pulses for the two relays 73 and 76 begin at the same time, they have different durations. The durations of said pulses are selected relative to each other so that the position of the surface of the molten steel'31 relative to the ingot mold 20 remains substantially unchanged during the remelting operation after the system has been started up. When all electric currents flowing through the fusible electrodes have decreased below predetermined minimum values, to which the contact ammeters have been set, and in addition the pulse relay 73 or 76 is closed (indicated in dotted lines), the above-described circuit causes the energization of the gearmotor 13 or 24 so that the electrode holder 11 and the fusible electrodes 10 are lowered by a predetermined distance and/or the ingot mold 20 is lifted by a predetermined distance. As a result, the holder 11 and the fusible electrodes 10 secured thereto are lowered step by step during the remelting operation whereas the mold-lifting carriage 23 and the ingot mold 20 secured thereto is lifted step by step during the remelting operation.

To enable also a fast movement of the abovementioned parts, each of the leads 72 and 75 includes a by-pass switch 74 or 77, which is connected in parallel to the pulse-controlled relay 73 or 76. Two threepole change-over switches, not shown, are connected in the supply leads R1, S1, T1 and R2, S2, T2, respectively, and permit of reversing and terminating the energization of the gearmotors 13 and 24, respectively,

' and of initiating and terminating its energization. During the above-mentioned start-up, the underside of the ingot mold contacts the bottom plate 40 and the change-over switch incorporated in the supply leads R1, S1, T1 is in its deenergizing position. Because the fusible electrodes 10 have equal cross-sectional surfaces, the contacts 71 of the ammeters 71 are set to the same current values.

For the sake ofcompleteness it should be noted that the ingot mold 20 is cooled with water which flows through the cavity 22 defined by the mold and an outer shell 21. Electrode holders for use in accordance with the invention may have a plurality of arms which carry respective fusible electrodes and are secured to the same lifting carriage.

The plant according to the invention may be provided with a plurality of ingot mold tubes which are secured to the same holder and in which respective electrodes are fused down.

Although the invention is illustrated and described with reference to one preferred embodiment thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment, but is capable or numerous modifications within the scope of the appended claims.

What is claimed is:

1. A plant for the electric slag refining of metals, which comprises an ingot mold,

a plurality of fusible electrodes,

a plurality of electrical supply conductors connected to respective ones of said electrodes and incorporating each a contact ammeter having a contact, which is arranged to operate when the current in the associated conductor is below a predetermined minimum, said contacts being connected in series,

an electrode holder carrying said fusible electrodes and movable to feed said electrodes into said mold, and

electrically operable feed drive means connected in series with said contacts and arranged to move said electrode toward said mold when all said contacts are in an operated condition.

'2. A plant as set forth in claim 1, in which said feed drive means comprise a drive motor and a contactor controlling the energization of said drive motor, said contactor-having an exciting winding,

a pulse-controlled relay is provided, which comprises a controlled relay contact, and

said contacts of said ammeters are connected in series with said exciting winding and said controlled relay contact.

3. A plant as set forth in claim 2, which comprises a by-pass switch connected in parallel to said controlled contact.

4. A plant as set forth in claim 1, in which said ingot mold'is disposed under said holder and adapted to be lifted and lowered and mold-lifting drive means are provided, which are connected in series with said contacts and arranged to lift said mold when all said contacts are in an operated condition.

5. A plant as set forth in claim 4, in which said feed drive means comprise a first drive motor and a first contactor controlling the energization of said first drive motor, said first contactor having a first exciting winding,

said lifting drive means comprise a second drive motor and a second contactor controlling the energization of said second drive motor, said second contactor having a second exciting winding,

first and second pulse-controlled relays are provided,

which comprise first and second controlled relay contacts, respectively,

said second exciting winding and said second relay contacts being connected in parallel to said first exciting winding and said first relay contact, which precedes said first exciting winding, and

said contacts of said ammeters are connected in series with said first and second exciting windings and said first and second relay contacts.

6. A plant as set forth in claim 5, which comprises first and second by-pass switches connected in parallel to said first and second relay contacts, respectively.

7. A plant as set forth in claim 6, in which said first and second pulse-controlled relays have first and second exciting windings, which are connected to a pulse generator arranged to feed said relays with pulses which begin at the same time and have different durations.

8. A plant as set forth in claim 7, in which said pulse generator is mechanically controlled.

9. A plant as set forth in claim 7, in which said pulse generator is electronically controlled.

10. A plant as set forth in claim 1, which is designed I electrodes connected to the respective conductors. 

1. A plant for the electric slag refining of metals, which comprises an ingot mold, a plurality of fusible electrodes, a plurality of electrical supply conductors connected to respective ones of said electrodes and incorporating each a contact ammeter having a contact, which is arranged to operate when the current in the associated conductor is below a predetermined minimum, said contacts being connected in series, an electrode holder carrying said fusible electrodes and movable to feed said electrodes into said mold, and electrically operable feed drive means connected in series with said contacts and arranged to move said electrode toward said mold when all said contacts are in an operated condition.
 2. A plant as set forth in claim 1, in which said feed drive means comprise a drive motor and a contactor controlling the energization of said drive motor, said contactor having an exciting winding, a pulse-controlled relay is provided, which comprises a controlled relay contact, and said contacts of said ammeters are connected in series with said exciting winding and said controlled relay contact.
 3. A plant as set forth in claim 2, which comprises a by-pass switch connected in parallel to said controlled contact.
 4. A plant as set forth in claim 1, in which said ingot mold is disposed under said holder and adapted to be lifted and lowered and mold-lifting drive means are provided, which are connected in series with said contacts and arranged to lift said mold when all said contacts are in an operated condition.
 5. A plant as set forth in claim 4, in which said feed drive means comprise a first drive motor and a first contactor controlling the energization of said first drive motor, said first contactor having a first exciting winding, said lifting drive means comprise a second drive motor and a second contactor controlling the energization of said second drive motor, said second contactor having a second exciting winding, first and second pulse-controlled relays are provided, which comprise first and second controlled relay contacts, respectively, said second exciting winding and said second relay contact being connected in parallel to said first exciting winding and said first relay contact, which precedes said first exciting winding, and said contacts of said ammeters are connected in series with said first and second exciting windings and said first and second relay contacts.
 6. A plant as set forth in claim 5, which comprises first and second by-pass switches connected in parallel to said first and second relay contacts, respectively.
 7. A plant as set forth in claim 6, in which said first and second pulse-controlled relays have first and second exciting windings, which are connected to a pulse generator arranged to feed said relays with pulses which begin at the same time and have different durations.
 8. A plant as set forth in claim 7, in which said pulse generator is mechanically controlled.
 9. A plant as set forth in claim 7, in which said pulse generator is electronically controlled.
 10. A plant as set forth in claim 1, which is designed for the electric slag refining of steel.
 11. A plant as set forth in claim 1, in which said predetermined minimum currents are approximately proportional to the cross-sectional areas of the fusible electrodes connected to the respective conductors. 